qos queue low-limit high-limit

Function

The qos queue low-limit high-limit command sets the upper and lower limits for buffering packets in a queue.

The undo qos queue low-limit high-limit command restores the default values of the upper and lower limits for buffering packets in a queue.

By default, the upper and lower limits for buffering packets in a queue are 78 and 68 buffer units, respectively. Each buffer unit is 360 bytes.

Only the S5735-L, S5735S-L, S5735S-L-M, S5735-S, S5735-S-I, and S5735S-S support this command.

Format

qos queue queue-index low-limit low-limit-pages high-limit high-limit-pages

undo qos queue queue-index [ low-limit low-limit-pages high-limit high-limit-pages ]

Parameters

Parameter	Description	Value
queue queue-index	Specifies the index of a queue.	The value is an integer in the range from 0 to 7.
low-limit low-limit-pages	Specifies the lower limit for buffering packets in a queue.	The value is an integer in the range from 1 to 5000. Each buffer unit is 360 bytes.
high-limit high-limit-pages	Specifies the upper limit for buffering packets in a queue.	The value is an integer in the range from the value of low-limit low-limit-pages to 5000. Each buffer unit is 360 bytes.

Views

Tail drop profile view

Default Level

2: Configuration level

Usage Guidelines

Usage Scenario

When congestion occurs, a switch uses the tail drop method. When the queue length reaches the upper limit, excess packets (buffered at the queue tail) are discarded until congestion is removed. You can run the qos queue low-limit high-limit command to set the upper limit and lower limit for buffering packets in a specified queue on an interface so that the queue has sufficient buffer, preventing packet loss.

When the size of packets in the queue buffer is always lower than or equal to the lower limit (low-limit low-limit-pages), the switch does not discard any packet. When the size of packets in the buffer increases and is greater than the lower limit:

If the size of packets in the queue buffer is always less than or equal to the upper limit (high-limit high-limit-pages), the switch does not discard any packet.
If the size of packets in the buffer increases gradually or even exceeds the upper limit, the switch discards the packets in the buffer until the size of packets in the queue does not exceed the lower limit.

Prerequisites

A tail drop profile has been created using the qos tail-drop-profile (system view) command. Only one tail drop profile can be created on the S5735-L, S5735S-L, S5735S-L-M, S5735-S, S5735-S-I, and S5735S-S.

Example

# Create a global tail drop profile named test, and set the lower limit and upper limit to 100 and 120 buffer units, respectively, for queue 0.

<HUAWEI> system-view
[HUAWEI] qos tail-drop-profile test
[HUAWEI-tail-drop-profile-test] qos queue 0 low-limit 100 high-limit 120